A COMPARATIVE STUDY OF INSTRUMENTAL LEARNING BY PRESCHOOL CHILDREN IN PAPUA NEW GUINEA AND AUSTRALIA1

Instrumental learning of preschool children in Papua New Guinea (PNG) and Australia (AUST) was compared using two tasks (imitative and nonimitative) and two rewards (social and nonsocial). There were no differences between the two groups in the rate of acquisition measure of trials to criterion. PNG children made more late responses during acquisition and, for nil responses, there were group x task and group x reward x task effects. In the extinction phase, there were two main effects for trials to criterion: PNG children were more resistant to extinction than AUST children, and there was greater persistence in responding after social reward regardless of nationality. Reward x group, reward x task, and reward x group x task interactions also were observed in the extinction trials to criterion. In addition, there were three main task effects during extinction for other responses: on the imitative task, more wrong responses were made, and on the nonimitative task, more extra responses and more paired responses were made. A subsidiary analysis compared the two culturally different but educationally similar groups comprising the PNG sample: no major differences were isolated in acquisition or extinction.     

An evaluation of methods for behavioral investigations of teleost audition

Auditory thresholds have been determined for the goldfish by six groups of workers and the data in the experiments varied by as much as 20–30 dB. In order to isolate the basis for this variability, auditory thresholds were determined using conditioned suppression of respiration and method of limits. These thresholds were very similar to those obtained with avoidance conditioning and a tracking method for threshold determination. Acoustic procedures were kept constant in the two series of experiments, and it appears that wide variation in auditory thresholds for goldfish shown in different experiments is due to acoustic conditions in the experiments.     

Stress and reproduction: central mechanisms and sex differences in non-rodent species

Despite extensive research, the mechanisms by which stress affects reproduction are unknown. Activation of stress systems could potentially influence reproduction at any level of the hypothalamo-pituitary gonadal axis. Nonetheless, the predominant impact is on the secretion of gonadotrophin releasing hormone (GnRH) from the brain and the secretion of the gonadotrophins, luteinizing hormone (LH) and follicle stimulating hormone (FSH), from the gonadotrophs of the anterior pituitary gland. When stress is prolonged, it is likely that secretion of the gonadotrophins will be suppressed but the effects of acute stress or repeated acute stress are not clear. Different stressors activate different pathways for varying durations, and the actions of stress vary with sex and are influenced by the predominance of particular sex steroids in the circulation. The mechanisms by which stress influences reproduction are likely to involve complex interactions between a number of central and peripheral pathways and may be different in males and females. To understand these mechanisms, it is important to determine the stress pathways that are activated by particular stressors and to establish how these pathways affect the secretion and actions of GnRH. Furthermore, there is a need to know how stress influences the feedback actions of gonadal steroids and inhibin.     

Author Index Volume 105

Authors Index

Author Index Volume 105     

Mechanisms and the Evidence Hierarchy

Evidence-based medicine (EBM) makes use of explicit procedures for grading evidence for causal claims. Normally, these procedures categorise evidence of correlation produced by statistical trials as better evidence for a causal claim than evidence of mechanisms produced by other methods. We argue, in contrast, that evidence of mechanisms needs to be viewed as complementary to, rather than inferior to, evidence of correlation. In this paper we first set out the case for treating evidence of mechanisms alongside evidence of correlation in explicit protocols for evaluating evidence. Next we provide case studies which exemplify the ways in which evidence of mechanisms complements evidence of correlation in practice. Finally, we put forward some general considerations as to how the two sorts of evidence can be more closely integrated by EBM.